When an electric field is applied to a liquid crystal display system, migration of ions occurs within the liquid crystal layer. Those ions will migrate so as to counteract the electric field, with cations moving towards the negatively charged plate and anions moving towards the positively charged plate, resulting in a net reduction of the electric field. Since the optical response of the liquid crystal is determined by the strength of the applied electric field, this results in sub-optimal liquid crystal behavior. Although it is sometimes possible to counteract the electric field reduction by applying additional voltage, this approach is undesirable both because it requires additional power and because side-effects such as chemical breakdown or defect formation could result. Thus, ionic conductivity is one of the most important metrics of liquid crystal materials for use in display applications, and great efforts are made when manufacturing liquid crystals to produce high purity materials.
In order to produce high purity liquid crystal materials ionic impurities must be removed. Various methods for removing ionic impurities have been disclosed. For example, Unexamined Japanese Patent Publication No. 64-87685 discloses a process for removing impurities using an adsorbent material such as silica gel, alumina, styrene-divinylbenzene porous polymer beads and on exchange resins. However, adsorption onto these materials is so strong that both ionic impurities and polar groups, chiral agents and the like are adsorbed. U.S. Pat. No. 5,540,857 allegedly overcomes these issues by using custom synthesized porous particles of imido group-containing compounds to purify liquid crystals. However, the custom synthesized compounds of the '857 patent are not readily available or affordable materials.